The present invention relates to data storage access and more specifically, this invention relates to dynamic record management in a system utilizing virtual storage access method (VSAM).
The virtual storage access method (VSAM) is a well-established access method that remains in current use with IBM® system architectures, and is frequently the basis for high-profile software packages such as financial management, personnel management, and other similar applications. VSAM offers an ease of utility that enables a broad range of users with diverse technical aptitude to access and utilize various applications and relevant data structures via the VSAM architecture.
For example, users and custom applications may access VSAM data sets through data definition (DD) statements written in a job control language (JCL) via dynamic allocation. Furthermore, custom access may be accomplished in online regions via the use of tools such as the customer information control system (CICS).
VSAM data set processing would, in most circumstances, benefit from an ability to make changes to this application code. Notably, when a VSAM data set is opened, certain attributes must be defined, for example, the number of buffers available for the data set to use. Since many VSAM data sets are large, complex, or both, the corresponding runtimes for data processing jobs are long, and may run into weeks or months of processing runtime, during which time the VSAM data sets remain open and unable to be changed using conventional methods.
In practice, computationally intensive data sets with such long runtimes experience fluctuations in processing efficiency resulting from corresponding fluctuations in system resource usage. For example, during normal business hours, system resources may be in a state of peak usage, and the number of available buffers (or other resources, such as memory, processors, etc.) are correspondingly low. Conversely, outside normal business hours, system resources may experience significantly less usage, and a correspondingly large amount of system resources may be idle. Thus, a user initiating a VSAM job during normal business hours may only have access to limited resources that do not accurately reflect actual system availability over the life of the job, resulting in undesirable inefficiencies.
Unfortunately, current VSAM tools strictly forbid processing characteristics from being changed after a data set is opened without stopping the job process, closing the data set, making the requested changes to static data, and subsequently resuming (or worse, restarting) the processing job anew. For dynamically allocated VSAM data sets, this type of record management tracing cannot be performed at all using standard VSAM tools—custom modules must be developed on an individual basis. This expensive and time-consuming process presents huge overhead and practical limitations on system administration because it requires constant system monitoring, as well as judgment from a human user(s), intervention, and sometimes necessitates code specific to the data set.